The invention concerns an aerosol generator especially for the generation of monodisperse aerosols such as calibration aerosols for the testing of measuring equipment and filters, aerosols for making streams visible or inhalation aerosols for medical purposes.
The production of highly concentrated monodisperse aerosols is based on the principle of controlled heterogeneous condensation: vaporized aerosol material condenses in the same fashion onto substantially smaller condensation nuclei. This forced condensation allows a high degree of monodispersity also at very high concentrations.
According to the principle of Sinclair-La Mer, nuclei are produced by an external nuclei source by vaporizing material from heated wires. Saturation of the gas stream with vapour of the aerosol material is achieved by a gas flow above the surface of the thermostated aerosol substance (heated at a temperature below the boiling point of the aerosol material). The particle size is adjusted by means of the temperature.
Following the Rappaport-Weinstock method, deliberately polluted aerosol material is passed through a jet spray and downstream heated to above the boiling point of the material to be used. The material evaporates completely. The impurities, which have not evaporated, serve as condensation nuclei for the heterogeneous condensation.
The particle size can be adjusted slowly and gradually by means of change in both temperature and choice of aerosol substance.
The aerosol generator developed by Prodi operates in accordance with the Sinclair-la-Mer-principle, whereby the condensation nuclei do not flow above the heated aerosol substance, rather they flow in a saturator through the aerosol substance, still in liquid form. The nuclei-vapour-mixture concentration and the particle size can also be adjusted by bypasssing this saturator, in addition to effecting adjustment by changing the temperature. The adjustment of the particle size is only possible over a small range. For higher requirements the degree of reproducibility is insignificant.